Engine tachometer



July 9, 1957 D. A. ARMSTRONG -ENGINE TACHOMETER Filed Feb. 13, 1956 INVENTOR. BAN/[l AAPM$W90N6 BY aim ATIURNEV United States Patent ENGINE TACHOMETER Daniel A. Armstrong, Thiensville, Wis., assignor to Kickhaefer Corporation, Cedarburg, Wis., a corporation of Wisconsin This invention relates to an engine tachometer to operate in association with the armature magnets of the magneto where such magnets are carried at the periphery of the flywheel.

An object of the invention is to provide a more dependable tachometer which does not require any mechanical connection of any operating part with any moving parts of the engine and which may be mounted within a cowl and removable therewith and having a mounting isolated from the vibration of the engine.

The drawings furnished herewith illustrate the best mode of carrying out the invention as presently contemplated and set forth hereinafter.

In the drawings:

Figure 1 is a side elevation of the upper part of an outboard motor with parts of the cowl broken away and sectioned and showing the tachometer housed within the cowl and in operative relation to the part of the magneto incorporated in the flywheel of the engine;

Fig. 2 is a plan view of the tachometer indicator arm and a portion of the flywheel which is broken away and sectioned to show one of the magnets of the magneto; and

Fig. 3 is a front elevation of the cowl showing the window and indicator arm for reading the rate of crankshaft rotation.

The outboard motor 1 shown in the drawings includes the engine 2 mounted and supported on the upper end of the housing 3, shown in part, and which encloses the drive shaft 4. The lower end of housing 3 carries an underwater propeller assembly, not shown, which is driven by engine 2 through shaft 4 connected at its upper end of the lower end 5 of the engine crankshaft extending downwardly into the upper end of housing 3.

Motor 1 includes the clamp bracket assembly 6 by which the motor is removably secured to the boat transom 7. The swivel pin 8 of bracket assembly 6 is located adjacent to and forwardly of drive shaft 4 and rotatably supports the drive shaft housing 3 so that the motor is dirigible with respect to the boat for steering on the vertical axis of the swivel pin. Vibration of the motor which occurs principally on the same axis referred to is absorbed by suitable cushion means, not shown, and such as that described and claimed in Patent No. 2,549,486, granted to E. C. Kiekhaefer, April 17, 1951 for Steering Mounting for Outboard Motors.

The upper end 9 of the engine crankshaft carries the flywheel 10 which has an outer annular depending rim 11 of considerable mass to provide the flywheel action. The magneto stator 12 shown diagrammatically is carried .at the top of the engine and disposed within the flywheel in operative relation to the permanent magnets 13 fixed to rim 11 within the flywheel and to rotate therewith.

According to the present invention, the tachometer utilizes the stray magnetic field which is usual and extends in lines along the outside of flywheel 10 and in the vicinity of magnets 13.

The indicator arm 14 carried on the small spindle 15 "ice is rotatably supported at opposite ends by the bracket 16 fixed to and within the cowl 17 which encloses engine 2. The permeable iron armature 18 carried by spindle 15 counterbalances arm 14 and the side of arma ture 18 facing flywheel 10 is curved to allow rotation on the axis of spindle 15 without interference with the flywheel. A reasonable clearance between the armature and flywheel places armature 18 in or near the path of the magnetic field of magnets 13 which extends beyond the outer dimensions of the flywheel rim 11 and tends to move the armature in the same direction.

The spring 19 having one end fixed to bracket 16 and the other end fixed to spindle 15, biases the spindle in the same direction of rotation as that of the flywheel and normally secures the armature 13 against the abutment 20 of bracket 16. Upon rotation of flywheel 10, the magnetic field effects a drag upon armature 18 which rotates spindle 15 against the action of spring 19 and moves arm 14 to a position reflecting the speed of rotation of the flywheel.

The window 22 formed in cowl 17 is transparent to allow the operator to see the position of the arm 14 and bears the markings 23 providing a calibration of the observed position of the arm to indicate the rate of rotation of flywheel 10 and speed of operation of the engine. As in speedometers utilizing a similar principle of operation, the rate of rotation of the flywheel is approximately proportionate to the displacement of the armature.

Bracket 16 may be supported directly by engine 2, if desired. Where the bracket is secured to the cowl, no mechanical connection between armature 18 and engine 2 is required which would otherwise interfere with the removal of cowl 17. The resilient support. of the cowl also may be provided to reduce noise if required without altering the operation of the device,

The bearings 24 of bracket 16 and supporting spindle 15 with indicator arm 14 and the armature 18 are employed in vertically spaced relationship to minimize the friction which otherwise interferes with the operation of the device.

The axis of spindle 15 is parallel to that of the flywheel 10 and the armature 18 is dimensioned so that in all positions a uniform mass is disposed in or near the path of the moving magnetic field. With the location of spindle 15 forwardly of the engine, the spindle is disposed in substantial or approximate alignment with the axis of vibration of the motor and the bearings 24 are accordingly relieved of unnecessary wear. By reason of this relationship spindle 15 and the parts supported by the spindle are relieved of a large degree of engine vibration which otherwise adversely affects the responsiveness of the armature 18 to the movement of the engine 13.

Various modes of carrying out the invention are contemplated as within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

I claim:

1. In combination with an engine having a flywheel and a magneto of the type wherein the magnets of the magneto are carried by the flywheel and the magnetic field incidentally extends beyond the flywheel, an indicator arm having bearing support means adjacent to said flywheel, a magnetizable member carried by said support means for rotation with said arm between limits and located and dimensioned so as to be generally uniformly subject to the influence of said magnetic field during at least a part of each revolution of the flywheel and subject to rotation in a given direction with respect to said bearing support means between said limits as in the course of engine operation, and a spring biasing said indicator arm and member in the other direction, the movement of said indicator arm a given distance within said limits indicating aproximately a given speed of operation of the engine. l

2. In an outboard motor, a cowl, an engine enclosed in the upper portion thereof, said engine having a flywheel within the cowl and including magnets providing a moving magnetic field incidental to engine ignition, bearing support means carried by said cowl, a magnetizable member carried by said support means for rotation between limits and located and dimensioned so as to be generally uniformly subject to the influence of said magnetic field and to movement therewith in a given direction upon each revolution of the flywheel as in the course of engine operation, an indicator arm associated with said member, and a spring biasing said indicator arm and member in the other direction, the movement of said indicator arm a given distance within said limits corresponding approximately to the speed of operation of the engine.

3. In an outboard motor, an engine having bearing support means for limited vibration of the motor on a vertical axis, said engine having a flywheel including magnets providing a moving magnetic field incidental to engine ignition, a cowl supported with said engine and enclosing the engine and flywheel, a rotatable spindle support carried by and within said cowl and generally above said first named bearing support means, a mag- V netizable member carried by said spindle and of dimensions with respect to the spindle so that a given portion of said member is uniformly within the influence of said magnetic field, a spring biasing said member in opposition to the movement of said member induced by said moving magnetic field, a transparent window formed within said cowl at the front of the motor, and an indicator arm carried by said spindle and observable through said window by the operator of the motor, the speed of operation of the engine being indicated by the degree of displacement of said indicator arm against the action of said spring, the axis of said spindle and the axis of vibration of the motor being parallel and approximately coincident whereby the said member and indicator arm carried by the spindle is generally unaffected by the vibration of the motor.

References Cited in the file of this patent UNITED STATES PATENTS 1,162,707 Nelson Nov. 30, 1915 2,649,848 Armstrong Aug. 25, 1953 FOREIGN PATENTS 203,729 Germany Oct. 26, 1908 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 2,798,472

Daniel A. Armstrong :1 the printed specification It is hereby certified that error appears i hat the said Letters of the above numbered patent requiring Correction and t Patent should read as corrected below.

Column 2, line 52, for "engine" read me magnets =-=Q Signed and sealed this 8th day of October 1957.

Attest: KARL H. .AXLDIE ROBERT C. wATsoN Conmissioner of Patents Attesting Officer 

